Different methods have been used to reinforce various polymers such as acrylic polymers. For example, crosslinking can impart greater shear strength and cohesive strength to the polymers. This crosslinking can be chemical or physical. Chemical crosslinking can include the introduction of a monomer having at least two groups selected from a polymerizable group capable of undergoing a polymerization reaction and a functional group capable of reacting or interacting with other groups within the polymer. Physical crosslinking methods have included the introduction of another polymeric moiety that is linked to the primary polymer but has the ability to phase separate from the primary polymer and form its own domain within the polymeric material. When the polymeric material is an adhesive material, the phase separated polymeric moiety can be selected to have a higher glass transition temperature than the primary viscoelastic polymer as described, for example, in U.S. Pat. No. 6,734,256 (Everaerts et al.), U.S. Pat. No. 7,255,920 (Everaerts et al.), and U.S. Pat. No. 5,057,366 (Husman et al.).
Bis-aziridine compounds have been used as chemical crosslinking agents in various polymer systems. Such compounds are described, for example, in U.S. Pat. No. 6,893,718 (Melancon et al.), German Patent No. 836,353 (Bestian), in an article of Bestian (J. Lieb. Ann. Chem., 566, 210-244 (1950)), in an article of Babenkova (J. of Applied Chemistry of the USSR, 40, 1715-1719 (1967)), and in an article of Kadorkina et al. (Bulletin of the Academy of Sciences of the USSR, 40, 780-783 (1991)).
Some aziridinyl-terminated polymers have been prepared as described, for example, in an article of Kobayashi et al. (Journal of Polymer Science: Part A: Polymer Chemistry, 43, 4126-4135 (2005)), Japanese Patent Publication JP4294369B2 (Kobayashi et al.), and European Patent Publication EP0265091A1 (Heftier et al.).
Blends of polyacrylates and polyamides have been described, for example, in U.S. Pat. No. 4,769,285 (Rasmussen) to prepare pressure-sensitive adhesives.